1. Field of the Invention
This invention relates to a peroxide crosslinked resin composition and electric wire and cable using the peroxide crosslinked resin composition. More particularly, the invention relates to a peroxide crosslinked resin composition excellent in blocking resistance in pellet form when in storage at ordinary temperature, capable of being extrusion molded for an organic peroxide including material, good in electrical properties when submerged in water, and capable of suppressing the emission of toxic gas when burnt. The invention also relates to an electric wire and a cable using the peroxide crosslinked resin composition.
2. Description of the Related Art
Awareness of environmental issues has been increasing worldwide, and there has been a demand for a halogen-free material, which is free from emission of halogen gas when burnt, and which suppresses carbon monoxide, which is one of toxic gases.
Meanwhile, electric wires or cables, which are wired in railway vehicles, automobiles, robots, etc., are required to have a high electrical insulation property, depending on an environment used. For example, when the electric wires or cables are exposed to water such as rainwater, seawater, etc., or when the electric wires or cables are used in a high temperature and high humidity environment, it is known that a non-polar polymer having no hydrophilicity is applied thereto (see, e.g. WO2008/108355).
Now, in general, rubber material is excellent in insulating performance. A molded product using a rubber material is produced through a crosslinking process with the addition of a peroxide. For example, when an electric wire and cable is fabricated, a rubber material is molded into the shape of the electric wire and cable with a temperature controlled extruder at a temperature at which no decomposition of an organic peroxide in the rubber material occurs, and subsequently is passed through a vulcanizing tube, resulting in the crosslinked electric wire and cable.
In order to produce a product which is good in electrical properties when submerged in water, it is preferable to singly use a nonpolar polymer including no filler, but when the nonpolar polymer is burnt, the amount of carbon monoxide emission is large, and response to crosslinking problems is insufficient. Further, since many of rubber materials generally have no melting point, and the rubbers adhere together at ordinary temperature and cause blocking, special equipment is required for processing into a ribbon shape, applying an anti-blocking agent and putting into a molding machine such as an extruder or the like.
A pellet shape may be proposed as a shape that is easy to mold in extrusion molding. When the rubber material is processed into pellets, due to an increase in contact area between the materials in comparison to the ribbons, blocking prominently manifests and molding becomes difficult. A material that can be molded into pellet form is generally a material having crystallinity, and many thereof, such as polyethylene or polypropylene, have a melting point of not lower than 100 degrees Celsius. When this material is extrusion molded with the addition of an organic peroxide, it may be scorched (or prematurely vulcanized), and therefore is constrained by molding conditions. Among the non-polar rubbers, an ethylene α-olefin copolymer can be a material having a melting point of not higher than 100 degrees Celsius, but has had the drawback of partial blocking when bagged, stacked and stored in a warehouse or the like for a long period of time.